Two-time defending champion Novak Djokovic suffered a shock defeat at the hands of Tommy Haas to leave Andy Murray in the box seat at the Sony Open in Miami.
Veteran German Haas completely outplayed the world number one for a 6-2 6-4 victory meaning Murray, who earlier beat Andreas Seppi by the same scoreline, is the highest seed left in the tournament going into the quarter-finals.
From 2-1 down in the first set, Haas won seven straight games to got 6-2 2-0 up and, though Djokovic eventually broke back to level, the 34-year-old held on for his first victory against a world number one since 1999.
In distinctly chilly conditions in the late match, there were hints of what was to come as Haas held his first two service games to love.
Haas then sealed the first break of the match as Djokovic netted, and the Serbian handed him another with a poor shot at net.
The 15th seed took the first set in less than half an hour, then kept on rolling with a break to open the second, in part thanks to a double fault from his opponent.
Djokovic saved break points in his next service game too, before holding to stop the rot, then pounced on some rare unforced errors from Haas to seal a break of his own and level at 3-3.
Haas broke again though at 4-4 and it proved decisive as he sealed the match at the second attempt with a forehand winner.
The German's prize is a last-eight meeting with 11th seed Gilles Simon, who beat Janko Tipsarevic in three sets.
Murray breezed into the quarter-finals, where he will face Marin Cilic, after cruising past 16th seed Seppi.
Murray has yet to drop a set in this tournament and this did not seem likely to change today as he was rarely tested by his Italian opponent, whose sole break point opportunity came in the final game.
The Briton felt the windy conditions worked to his advantage.
"It was swirling a little bit at the start and he made more unforced errors than he usually does," he told the Independent. "I was able to track down a lot of his balls because he wasn't timing his shots that well.
"But he started going for his shots more in the second set and made it tough for me."
A limp forehand into the net immediately gave Murray two break points in the opening game and another unforced error from Seppi gave the world number three the initiative.
Seppi, who reached a career-high 18th in the world in January this year, won just four points on Murray's serve in the first set and was broken again in the seventh game as the US Open champion put one foot into the next round.
The second seed wasted three break point opportunities at the start of the second set before Seppi steadily settled.
The 29-year-old had a slight hope of getting back into the match when Murray found himself 4-3 and 0-30 down on his serve before storming back to level.
In the very next game, Murray earned his fourth break point opportunity of the set and he would not be denied this time as Seppi crashed a forehand into the net.
The Briton had a bit of a wobble serving out the match and although Seppi had an opportunity to break straight back, Murray sealed victory with his first match point, booking a meeting with ninth seed Cilic who beat Jo-Wilfried Tsonga 7-5 7-6 (7/4).
There were also wins for the third and fourth seeds, David Ferrer and Tomas Berdych, as well as Richard Gasquet and Jurgen Melzer.
In the women's draw, Serena Williams matched Steffi Graf's record for the number of match wins in this tournament, a 6-3 7-6 (7/5) win over Australian Open finalist Li Na in the quarter-finals seeing the American claim her 59th victory in the Miami Masters.
"I'm excited," said the five-time champion in her on-court interview. "It's just great.
"Every day I play here is a surprise for me because I enjoy it so much. I enjoy the great crowd and I'm just happy to still be here."
Williams will next face Polish fourth seed Agnieszka Radwanska, who produced an astonishing shot in the second set to help her beat Belgium's Kirsten Flipkens 4-6 6-4 6-2.
Wrong-footed by a net cord, Radwanska spun more than 180 degrees and stuck out her racquet for an improvised volley winner, leaving her opponent staring in disbelief.